If a temperature of fuel in a vehicle fuel tank is equal to or higher than a boiling point according to the external environment, as shown in FIG. 1, the fuel is boiled and thus bubbles are generated.
At this time, in order to measure a liquid level of the fuel in the vehicle fuel tank, when an ultrasonic signal is transmitted from an oscillator for measuring a distance to a fuel surface using an ultrasonic sensor, a diffused reflection or scattering phenomenon due to bubbles occurs.
As shown in FIG. 1, when the diffused reflection or scattering phenomenon occurs due to the bubbles, the ultrasonic signal reflected from a response unit may not be received, and therefore it is recognized that there is no fuel, such that there is a problem that it is difficult to accurately measure the liquid level.
Korean Patent Laid-Open Publication No. 10-1999-0058443 (“Apparatus and method for measuring fuel amount using ultrasonic sensor”, hereinafter referred to as related art document 1) discloses an apparatus and a method for measuring a fuel amount remaining in a fuel tank by measuring a distance to a fuel surface using an ultrasonic sensor installed on an inner wall of the fuel tank.
However, the related art document 1 does not disclose a method for overcoming a measurement error of an ultrasonic sensor when fuel boils and thus bubbles are generated.